Melt-processable block copolyesterimide and method for manufacturing it

ABSTRACT

A melt-processable block copolyesterimide comprising the repeating units (I), (II) and (III) and, optionally, a repeating unit (IV), wherein (I) is a repeating unit of the formula ##STR1## wherein R is an aliphatic polyether chain and/or a polysiloxane chain; (II) and (III) are repeating units of the formulas ##STR2## wherein Z is hydrogen, alkyl, alkoxy, aryl, halogen and w is zero or one; and (IV) is a repeating unit of the formula ##STR3## wherein Z&#39; is hydrogen, alkyl, alkoxy, aryl or halogen and the phenylene ring is substituted in by Z&#39; in the m- or p-positions. The repeating unit of formula (I) is present in an amount of 5 to 50 mole-%, the repeating unit of formula (II) is present in an amount of 10 to 80 mole-%, the repeating unit of formula (III) is present in an mount of 5 to 50 mole-% and the repeating unit of formula (IV) is present in an amount of 0 to 45 mole-% of the block copolyesterimide. The polymer according to the invention has liquid crystalline properties and it can be used as thermoplastic elastomer component of polymer compounds.

The present invention relates to block copolymers and to a method formanufacturing them.

Liquid crystalline polymers are polymers which in melt state exhibitoptical anisotropy. The strength and stiffness of many thermoplasticscan be substantially improved by blending them with thermotropic,main-chain liquid crystalline polymers. This is because the liquidcrystalline polymers form fibres which orientate in the flow directionof the thermoplastic matrix melt. As a result there is an improvement ofthe mechanical properties, such as tensile strength and modulus ofelasticity, of the thermoplastic in this direction. Often, the additionof the liquid crystalline polymer also improves the heat resistance anddimensional stability of the thermoplastics and makes it easier toprocess them. Liquid-crystal polymers are, for the above reasons, beinginvestigated widely.

The actual liquid crystal in liquid crystalline polymers is formed by arigid structural unit called a mesogen. Mesogens are generally formed bytwo or more linearly substituted ring units linked to each other via ashort, rigid bridging group known as a spacer. As examples of mesogenicstructural units, the polyester groups formed by hydroxy benzoic acid,terephthalic acid and hydroquinone should be mentioned. Liquid-crystalpolymers can be divided into two main categories, viz, main-chain andside-chain liquid-crystal polymers, depending on whether the mesogenicgroups are located in the main chain or in the side chain. Main-chainliquid crystalline polymers are generally polymers of highly rigidcharacter whose stable crystalline structure can only be melted by usingabundant energy. Therefore, their melting occurs at high temperatures,whereby thermal decomposition is simultaneously involved.

As far as liquid crystalline polymers and their properties areconcerned, reference is made to the review article by Chung et al. inHandbook of Polymer Science and Technology, 2 (1989) pp. 625 to 675.

Block polyesterimides with liquid crystalline properties are known inthe art. Said polymers have been described in, for instance, U.S. Pat.Nos. 4,727,129, 4,728,713 and 4,728,714. The prior art aromaticcompounds have, according to the patent specifications, good strengthand heat and wear resistance. At temperatures below 320° C. the polymersprovide melts which form liquid crystalline fibers. The prior ancompounds do not, however, have the properties needed for thermoplasticelastomer applications, such as good flexibility at low temperatures andthermal and hydrolytical stability.

It is an object of the present invention to solve the problems relatingto the prior an and to provide an entirely novel kind of a liquidcrystalline polyesterimide, which can be used as a thermoplasticelastomer component in polymer compounds.

According to the present invention, there is provided a novel (A-B)_(t)-type block copolymer wherein t is an integer, typically about 3 to 100,the second block (B) being formed by a rigid aromatic polyester segment.According to the invention, block A comprises a flexible trimellitimideterminated polyether or a polysiloxane. The structure of block A istypically ##STR4## wherein R stands for a polyether or polysiloxane.

In more detail, the liquid crystalline polymer according to theinvention is mainly characterized by what is stated in thecharacterizing part of claim 1.

The method according to the invention is, again, characterized by whatis stated in the characterizing part of claim 10.

The compounds according to the invention are characterized by what isstated in the characterizing part of claim 14.

To complete the survey of the prior art, it should be mentioned thatblock copolymers containing polyether, in particularpoly(tetrahydrofuran) are known per se. Reference is made to the articleby Wang and Lenz in Polymer Engineering and Science 31 (1991) pp. 739 to742!. The structure of this known polymer is ##STR5## and it does notcontain a polyesterimide structure according to the present invention.Its properties are also different from those of the present polymers.

High molecular weight diimide diacids of tricarboxylic acids are alsoknown per se. We refer to European Published Patent Application No. 0180 149, which describes the preparation of these compounds in a dipolaraprotic solvent, such as xylene, at temperatures in the range of 150° to300° C. The process of the present invention differs from the prior artin the sense that Block A of the compound is prepared by using a cyclicether (dioxane), which makes it possible to lower the temperature to100° C.

U.S. Pat. No. 4,556,705 discloses thermoplastic poly(ether/imide/esters)containing structures similar to the ones disclosed in the EuropeanPublished Patent Application No. 0 180 149. The compounds are not liquidcrystalline. From the U.S. publication it appears that component a ofthe polymers is comprised of one or more low molecular weight C₂ to C₁₅aliphatic or cycloaliphatic diol(s). The aromatic dicarboxylic acids ofthe known compounds preferably comprise dimethyl terephthalate. As thedescription given below will show in more detail, the present polymersdiffer from the compounds according to the U.S. Pat. No. 4,556,705 inthat, for instance, the aromatic diols contain at least 18 carbon atoms(3 phenylene rings), i.e. they are complex diols having an aromaticpolyester chain. Furthermore, the polymers, wherein the molecular weightof the poly(THF) is about 1000 to 2000, are liquid crystalline. Polymerswith poly(THF) units having molecular weights in excess of 2000 areisotropic. The process for preparing the present polymers also differsfrom the process disclosed in the U.S. reference. Thus, the polymersaccording to the invention are prepared by transesterification ofacylated aromatic diols with aromatic dicarboxylic acids. In thisreaction, acetic acid is formed. Surprisingly, said strong acid does notgive rise to chain scission of the poly(oxyalkylene) chain at the highreaction temperature applied, which can be shown by ¹³ C NMRspectroscopy.

The rigid segment (B) of the novel block copolymers is formed by anaromatic polyester structure commonly used in liquid crystallinepolymers. We refer to what was stated above concerning the mesogenicgroups and to the structural formulas given below.

Finally, as far as the prior art is concerned, it should be mentionedthat DE Published Patent Application No. 3,516,427 disclosesthermotropic polyesterimides, which contain C₈ to C₁₆alkylene-α,ω-bis-trimellitimide units. In these known polyesterimidesthe mesogenic units contain only one phenylene ring, whereas themesogenic units of the present polymers preferably contain at least 3phenylene rings. The prior art polymers do not, either, contain spacerssimilar to the ones used in the invention, i.e. polyoxyalkylene orpolysiloxane segments; the alkylene units used are relatively shortchained (C₁₆) and, thus, differ essentially from, for instance, thepoly(THF) units used in the invention.

The polymers according to the invention contain polyoxyalkylene orpolysiloxane units, trimellitimide units and large polyester blocks,which consist of phenylene rings attached to each other with esterbonds. The polymers have elastomeric and thermotropic properties incombination with the properties of the polyoxyalkylene (polysiloxane),trimellitimide and the aromatic polyester chain. The advantageousproperties of the polymers are a result of the combination of thestructural elements shown below.

According to an embodiment of the invention, polyesterimide blockcopolymers are provided having repeating units of formulas (I), (II) and(III) and possibly a repeating unit of formula (IV), wherein (I) is arepeating unit of the formula ##STR6## wherein R is at least one of analiphatic polyether chain and a polysiloxane chain;

(II) is a repeating unit of the formula ##STR7## (III) is a repeatingunit of the formula ##STR8## wherein Z is hydrogen, alkyl, alkoxy, arylor halogen, and w is zero or one; and

(IV) is a repeating unit of the formula ##STR9## wherein Z' is hydrogen,alkyl, alkoxy, aryl or halogen and the phenylene ring is substituted inby Z' m- and p-positions.

According to the invention, in the copolymer according to formula (I)the repeating unit of formula (I) is present in an amount of 5 to 50mole percent of the block copolyesterimide, the repeating unit offormula (II) is present in an amount of 10 to 80 mole percent of theblock copolyesterimide, the repeating unit of formula (III) is presentin an amount of 5 to 50 mole percent of the block copolyesterimide, andthe repeating unit of formula (IV) is present in an amount of 0 to 45mole percent of the block copolyesterimide.

The polyether "R" can, for instance, comprise poly(methylene oxide),poly(ethylene oxide) or poly(butylene oxide). Alkyl- andaryl-substituted groups may be mentioned among the polysiloxanes.

Thus, according to a preferred embodiment of the invention R comprises arepeating unit of formula (V) ##STR10## wherein X is hydrogen or methyl,n is 0, 1, 2 or 3, and m is an integer of 3 to 65, or optionally,

a repeating unit of formula (VI) ##STR11## wherein Y is alkyl or aryl,preferably methyl and p is an integer of 5 to 30.

In particular, R is a poly(butylene ether) which in the following willbe called poly(tetrafuran) (polyTHF), the structure of segment A being:##STR12## wherein n is an integer in the range of 3 to 65, preferably 10to 30.

In the below examples, a poly(tetrahydrofuran) with a comparatively lowmolecular weight of about 1000 to 2000 has been used.

Within the scope of the present application, the term "halogen" denotesfluorine, chlorine, bromine or iodine, preferably chlorine, bromine oriodine, in particular chlorine or bromine. "Alkyl" is preferably astraight- or branched-chained, saturated lower alkyl group containing 1to 6, preferably 1 to 4 carbon atoms. The following examples can belisted: methyl, ethyl, n-propyl, isopropyl, n-butyl, sek-butyl,tert-butyl (1,1-dimethylethyl) and 2-methylbutyl. "Alkoxy" represents alower alkoxy containing preferably 1 to 6 carbon atoms, in particular 1to 4 carbon atoms, such as methoxy, ethoxy, propoxy and tert-butoxy."Aryl" is a monovalent aromatic group, such as phenyl and benzyl.

According to a second preferred embodiment of the invention there isprepared a melt-processable block copolyesterimide (a-b-c), whichcomprises the reputing units of formula VIII ##STR13## wherein z ishydrogen, alkyl, aryl or halogen, r is for instance 4, m is 3 to 65 andw has the same meaning as above, and a, b and c represent the respectivemolar amounts of each of the repeating units of the blockcopolyesterimide and the molar amounts of each symbol "a", "b" and "c"correspond to the following formulas:

    a+b+c=1 and a=b

In particular, in the formulas presented above w preferably stands for 0and a, b and c represent the following concentration ranges:

a=0.05 to 0.5

b=0.05 to 0.5

c=0.1 to 0.8

A particularly preferred structure is represented by an embodiment,wherein w is 1 and a, b and c represent the above concentration ranges.

Of the polymers according to the invention, the structure of the monomerof a preferred polymer is depicted in formula (IX): ##STR14## wherein nis an integer 3 to 65, x is 10 to 100 and y is 20 to 160.

Typically the block copolyesterimides described above are capable offorming an anisotropic melt phase at temperature below 250° C., whichmakes it possible to use them for preparing melt-processable polymerblends, i.e. polymer compounds.

In special cases (for instance when the molecular weight of thepoly(THF) is higher than 2000 and the content of aromatic units is low,and in case of polymers prepared from isophthalic acids), the productsare not liquid crystalline. These polymers can, however, also be usedfor the preparation of various compounds because they have elastomericproperties.

The block copolyesterimides according to the invention can be preparedby mixing a carboxyl-terminated compound of formula (X) ##STR15##wherein R corresponds to formula V or formula VI given above, with apara- and/or meta-acetoxycarboxylic acid of formula (XI) ##STR16## andwith a diacetoxy compound of formula (XII) ##STR17## wherein w and zhave the same meaning as above, and, optionally, with aromaticdicarboxylic acids of formula (XIII) ##STR18## wherein z' has the samemeaning as above, then fusing the mixture, splitting off the acetic acidformed, and condensing the mixture under reduced pressure attemperatures in the range of 150° to 300° C.

According to a second embodiment, the block copolyesterimides accordingto the invention are prepared by mixing a carboxyl-terminated compoundaccording to formula (X), wherein R represents a group of formula V orformula VI, with a para- and/or meta-acetoxycarboxylic acid of formula(XI) and an acetoxy-terminated compound of formula (XIV) ##STR19##(wherein z and w have the same meaning as above), then fusing themixture, splitting off the acetic acid formed and condensing the mixtureunder reduced pressure at a temperature in the range of 150° to 300° C.

In particular a carboxyl-terminated compound of formula (X) is preparedby reacting an amino-terminated compound of formula (XV)

    H.sub.2 H--R--NH.sub.2                                     (XV)

wherein R has the same meaning as above with a trimellitic anhydride indioxane, followed by removal of the dioxane under reduced pressure andthermal treatment.

According to a preferred embodiment of the invention, the polymerizedmonomer is obtained by either condensing two moles of a para- ormeta-hydroxycarboxylic acid of formula (XVI) ##STR20## with one mole ofan acetoxy compound of formula (XII), followed by acylation of thehydroxyl groups, or

by condensing in pyridine two moles of an acetoxy carboxylic acidchloride derived from a compound of formula (XI) with one mole of adihydroxy compound of formula (XVII) ##STR21## wherein z and w have thesame meaning as above, followed by precipitation and extraction inmethanol and drying.

The polymer described herein is well suited to use in blends withthermoplastics, in particular with polyolefins and polyolefiniccopolymers, and with polyesters. As examples of the polyolefins, thefollowing should be mentioned: polyethylene, polypropylene, polybutene,polyisobutylene, poly(4-methyl-1-pentylene) including copolymers ofethylene and propylene (EPM, EPDM) and chlorinated and chlorosulfonatedpolyethylenes. Alternative matrix polymers comprise the correspondingpolyalkenes containing styrene, acryl, vinyl and fluoroethyl groups, aswell as various polyesters, such as poly(ethylene terephthalate),poly(butylene terephthalate) and polycarbonates. In addition to theabove mentioned, the polyester according to the invention can be blendedwith polyamides and polyethers.

The thermoplastic/liquid crystalline polymer blends according to theinvention can be prepared by methods known per se.

The mixing methods are either batch or continuous processes. As examplesof typical batch mixers, the Banbury mixer and the heated roll mill maybe mentioned. Continuous mixers are exemplified by, for instance, theFarrel mixer, and single- and twin-screw extruders. Preferably single-or twin-screw extruders are used for blending the liquid crystallinepolymer with the thermoplastic. The liquid crystalline polymers areblended with the thermoplastics either by first premixing the liquidcrystalline polymers with the thermoplastics in a twin-screw extruderand then processing them in an injection molding machine or,alternatively, by processing them by injection molding or extrusionwithout premixing.

By attaching polysiloxane or polyether units, in particular units ofpoly(tetrahydrofuran) as soft segments to the block copolymer of theinvention, thermally stable thermoplastic elastomers are providedexhibiting excellent resistance to wear and good dynamical properties.They also have excellent elastomeric properties at low temperatures. Atthe same time, it has surprisingly been found that the polymersaccording to the invention have a better heat resistance thanelastomeric materials generally, which makes it possible to use productsfabricated from the polymers in elastomeric applications wherein goodstrength is required at high temperatures. The polymer or blends thereofcan be used in particular as thermoplastic elastomers in injectionmolded, blow molded. extruded and deep drawn articles, profiles, films,robes, pipes, cables and sheets. Flexible containers and car partsfitted under the hood of the engine can be particularly mentioned asfields of application of the present polymers.

The polymers according to the invention can also be employed ascompatibilizers in blends of thermoplastic polymers and liquidcrystalline polymers, said polymers being capable of improving theimpact strength of said blends without substantially impairinglongitudinal strength. The compatibilizer applications include inparticular blends of liquid crystalline polymers with polyolefins,polyether, polyesters, polyamides or polyimides. There can be one ormore thermoplastic polymers in the blends.

Next, the invention will be examined in more detail with the aid of anumber of non-limiting working examples:

EXAMPLE 1 Preparation of Trimellitimide-terminated Poly(THF)

In a three-necked flask of 1 litre capacity equipped with a mechanicalstirrer and a reflux condenser, the following reactants were charged:

40 g of poly(THF)-diamine with a molecular weight of 1100 g/mole (driedat 50° C. for two days in a vacuum oven),

13.6 g of trimellitic anhydride and

800 ml of dioxane (dried over KOH and distilled).

The reaction mixture was stirred under reflux for 8 hours. Aftercooling, dioxane was removed by evaporation in a vacuum rotator at 50°C. The crude product was imidized at 180° C. for 30 min. with a vacuumof 2 Torr.

A light-brown resin was obtained with a molecular weight of 1200 g/molemeasured by titration of the COOH-end groups.

EXAMPLE 2

This example illustrates polycondensation of trimellitimide-terminatedpoly(THF)1000 with an acetoxy-terminated trimer designed HBA-HQ-HBA ofthe following formula and p-acetoxybenzoic acid. ##STR22## (thesynthesis of this monomer is given by W. R. Krigbaum, R. Kotek, T.Ishikawa. H. Hakemi. J. Preston: Europ. Polym. J. 20, 3. 225-235 (1984)and D. van Luyen. L. Strzelecki: Europ. Polym. J. 16, 303 (1980)

The polycondensation equipment employed was a three-necked flask of 100ml capacity equipped with a stirrer, N₂ -inlet tube and distillationhead. The equipment was heated by means of a metal bath.

To the above reactor, the following reactants were charged:

a) 8.6 g of trimellitimide-terminated poly(THF)1000 (7.60 mmoles),

b) 3.30 g of acetoxy-terminated HBA-HQ-HBA (7.60 mmoles) and

c) 1.18 g of p-acetoxybenzoic acid (6.51 mmoles)

At ambient temperature, the reaction flask is evaporated and filled withnitrogen three times. Thereafter, the flask is immersed into a metalbath of a temperature of 220° C. The reaction is carried out understirring and a slight nitrogen stream at 220° C. for 5 minutes. Afterthis time, the temperature of the metal bath is raised to 260° C. (in 10minutes). The polycondensation is carried out at 260° C. for a further30 minutes, and finally for 30 minutes at 260° C. under a vacuum of 1 to2 Torr. During the whole process, distillation of acetic acid can beobserved. The resulting polymer is a light-brown rubber-like product.

The relative viscosity was measured in a phenol/1,1,2,2-tetrachlorethanemixture (1:1 by vol) with a polymer concentration of 0.5 g/dl by meansof an Ubbelohde capillary. viscosimeter (capillary Ia) at 25° C. Theinherent viscosity is calculated by the following formula: ##EQU1##

The inherent viscosity of the resulting polymer was 0.757 dl/g. Themolecular weights measured by GPC with polystyrene standard were foundto be M_(n) =95,000 g/mole and M_(w) =180,000 g/mole).

The polymer, when examined by means of polarizing microscopy equippedwith a heating stage, showed at temperatures of 160° C. a strongbirefringence as indication of a thermotropic liquid-crystallinebehaviour of the polymer.

EXAMPLE 3

In the same equipment and following the same procedures as in Example 2,the following reactants were polymerized:

a) 10.26 g of trimellitimide-terminated poly(THF)1000 (9.8 mmoles),

b) 2.65 g of diacetoxy diphenyl (9.8 mmoles) and

c) 3.53 g of p-acetoxybenzoic acid (19.6 mmoles)

The polymer obtained was not soluble in phenol/tetrachlorethane. Whensubjected to DSC analysis, the melting was found to be at 211° C. (peakmaximum) with a melting enthalpy of 2.6 J/g. The melting temperature wasfound to be at 160° C. by polarizing microscope. The polymer forms aliquid-crystalline phase in the melt.

EXAMPLE 4

In the same equipment and following the same procedures as in Example 2,the following reactants were polymerized:

a) 5.832 g of trimellitimide-terminated poly(THF)1000 (5.66 mmoles),

b) 1.11 g of hydroquinone diacetate (5.66 mmoles) and

c) 3.056 g of p-acetoxybenzoic acid (0.17 mmoles)

The resulting rubber-like brown product has a very, low meltingtemperature of 115° C. and an isotropization temperature of 140° C. asobtained by polarizing microscopy. It showed under crossed polarizers aliquid-crystalline melt.

EXAMPLE 5 Preparation of an Acetoxy-terminated Precursor forPolycondensation

In a three-necked flask of 500 ml capacity equipped with a mechanicalstirrer, N_(z) -inlet tube and distillation head the following reactantswere charged:

a) 65.50 g of p-hydroxybenzoic acid (0.475 moles) and

b) 46.51 g of hydroquinone diacetate (0.237 moles)

The flask is evaporated and thereafter filled with dried nitrogen forthree times at ambient temperature. After this procedure, the flask isimmersed into a metal bath of a temperature of 260° C. The reaction iscarried out for 30 minutes at 260° C. under stirring and slight nitrogenstream. After this time, the temperature of the metal bath is increasedto 270° C. and the reaction is continued for 90 minutes at thistemperature. At the end of the reaction, the flask is removed from thebath. After cooling down, the reaction product is removed from the flaskand powdered in an analysis mill.

The resulting powder is charged together with 500 ml of acetic anhydridein a three-necked flask of 1 l capacity, equipped with a mechanicalstirrer and a reflux condenser. The reaction mixture is refluxed understirring for 12 hours. After cooling, the resulting white product isfiltered off, washed with distilled water and dried in a vacuum oven for8 hours.

The IR spectrum of the product shows complete acetylation without freeOH-groups (typical acetoxy-signals at 1750, 1740, 1370, 1210 and 1080cm⁻¹).

EXAMPLE 6

In the same equipment and following the same procedures as in Example 2,the following reactants were polymerized:

a) 4.76 g of trimellitimide-terminated poly(THF)1000 (4.55 mmoles) and

b) 1.98 g of the acetoxy-terminated precursor according to Example 5(4.55 mmoles)

The resulting product has a melting temperature of 150° C., anisotropization temperature of 185° C. and shows in the range of 150° C.to 185° C. a liquid-crystalline melt observed by polarizing microscopy.Its inherent viscosity in phenol/tetrachlorethane is 0.78 dl/g.

EXAMPLE 7

In the same equipment and following the same procedures as in Example 2,the following reactants were polymerized:

a) 4.07 g of trimellitimide-terminated poly(THF) 1000 (3.1 mmoles),

b) 0.52 g of terephthalic acid (3.1 mmoles),

c) 2.69 g of acetoxy-terminated HBA-HQHBA according to Example 2 (6.2mmoles) and

d) 1.49 g of p-acetoxybenzoic acid (8.27 mmole).

The temperature of the metal bath in the vacuum phase of thepolycondensation was kept at 270° C.

The resulting grey product has a melting temperature of 180° C. andshows a liquid-crystalline phase at temperatures up to 350° C. It is notsoluble in phenol/tetrachlorethane.

EXAMPLE 8

Following the procedure given in Example 1, 44.12 g of aminoterminatedsilicone (0.05 mole) of formula 2 of a molecular weight of approximately880 g/mole given by titration of amino end groups is reacted with 0.1moles of trimellitic anhydride in 800 ml of dried, distilled dioxane byrefluxing the reaction mixture for 8 hours. ##STR23##

After removing the solvent, a yellow resin was obtained with a molecularweight of 1070 g/mole measured by titration of COOH-end groups.

EXAMPLE 9

In the same equipment and following the same procedures as in Example 2,the following reactants were polymerized:

a) 4.5 g of trimellitimide-terminated silicone (4.2 mmoles),

b) 1.83 g of acetoxy-terminated HBA-HQ-HBA according to Example 2 (4.2mmoles) and

c) 1.52 g of acetoxybenzoic acid (8.4 mmoles).

The resulting light brown brittle polymer has an inherent viscosity of0.65 dl/g in phenol/tetrachlorethane. The polymer melting temperature isfound to be at 150° C. The polymer forms a liquid-crystalline melt phasewithout isotropization up to temperatures of 350° C.

We claim:
 1. A melt-processable block copolyesterimide comprisingrepeating units (I), (II) and (III) and, optionally, a repeating unit(IV), wherein:(I) is a repeating unit of the formula ##STR24## wherein Ris at least one of an aliphatic polyether chain and a polysiloxanechain; (II) is a repeating unit of the formula ##STR25## (III) is arepeating unit of the formula ##STR26## wherein Z is hydrogen, alkyl,alkoxy, aryl or, halogen, and w is zero or one; and (IV) is a repeatingunit of the formula ##STR27## wherein Z' is hydrogen, alkyl, alkoxy,aryl or halogen and the phenylene ring is substituted by Z' in the m- orp-positions; whereinthe repeating unit of formula (I) is present in anamount of 5 to 50 mole percent of said block copolyesterimide; therepeating unit of formula (II is present in an amount of 10 to 80 molepercent of said block copolyesterimide; the repeating unit of formula(III) is present in an amount of 5 to 50 mole percent of said blockcopolyesterimide; and the repeating unit of formula (IV) is present inan amount of zero to 45 mole percent of said block copolyesterimide. 2.The block copolyesterimide according to claim 1, wherein, in saidformula (I), R comprises repeating units of the formula (V) ##STR28##wherein X is hydrogen or methyl, n is 0, 1, 2 or 3, and m is an integerof 3 to 65, or, optionally,repeating units of the formula (VI),##STR29## wherein Y is alkyl or aryl and p is an integer in the rangefrom 5 to
 30. 3. A block copolyesterimide according to claim 1, whereinsaid block copolyesterimide is capable of forming an anisotropic meltphase at a temperature of approximately 250° C. or less.
 4. Amelt-processable block copolyesterimide consisting essentially of therepeating units represented by the formula (VIII) ##STR30## wherein z ishydrogen, alkyl, aryl or halogen, r is 4, m is an integer ranging from 3to 65, w is 0 or 1, and a, b and c represent the respective molaramounts of each of the repeating units of the block copolyesterimide andthe molar amounts of a, b and c conform to the followingrelationships:a+b+c=1 and a=b.
 5. A block copolyesterimide according toclaim 4, wherein w is 0 and a, b and c represent the followingconcentration ranges:a=0.05 to 0.5 b=0.05 to 0.5 c=0.1 to 0.8.
 6. Ablock copolyesterimide according to claim 4, wherein w is 1 and a, b andc represent the following concentration ranges:a=0.05 to 0.5 b=0.05 to0.5 c=0.1 to 0.8.
 7. The block copolyesterimide according to claim 4,wherein said block copolyesterimide is capable of forming an anisotropicmelt phase at a temperature of approximately 250° C. or less.
 8. Amelt-processable block copolyesterimide, which is capable of forming ananisotropic melt phase at a temperature of approximately 250° C. orless, characterized in that it corresponds to the formula (A-B)_(t),wherein t is an integer 3 to 100, B represents a rigid aromaticpolyester segment and A comprises a flexible trimellitimide terminatedpolyether or polysiloxane.
 9. The block copolyesterimide according toclaim 8, wherein A represents a unit of formula (I) ##STR31## wherein Rrepresents a unit of formula (V) ##STR32## wherein X is hydrogen ormethyl, n is 0, 1, 2 or 3, and m is an integer ranging from 3 to 65, ora unit of formula (VI), ##STR33## wherein Y is alkyl or aryl and p is aninteger ranging from 5 to
 30. 10. A process for preparingmelt-processable block copolyesterimides, characterized by mixing acarboxyl-terminated compound of formula (X) ##STR34## wherein Rcomprises repeating units of formula (V), ##STR35## wherein X ishydrogen or methyl, n is 0, 1, 2 or 3, and m is an integer ranging from3 to 65, or, optionally, repeating units of formula (VI) ##STR36##wherein Y is alkyl or aryl and p is an integer ranging from 5 to 30,with a para- and/or meta-acetoxycarboxylic acid of formula (XI)##STR37## and with a diacetoxy compound of formula (XII) ##STR38##wherein w is 0 or 1 and Z represents hydrogen, alkyl, alkoxy, aryl orhalogen, and, optionally, with aromatic dicarboxylic acids of formula(XIII) ##STR39## wherein Z' represents hydrogen, alkyl, alkoxy, aryl orhalogen, then fusing, splitting off the acetic acid formed, andcondensing the mixture under reduced pressure at temperatures rangingfrom 150° C. to 300° C.
 11. The process according to claim 10, whereinthe carboxyl-terminated compound of formula (X) ##STR40## is prepared byreacting an amino-terminated compound of formula (XV) wherein R informulas (X) and (XV) comprises repeating units of formula (V),##STR41## wherein X is hydrogen or methyl, n is 0, 1, 2 or 3, and m isan integer ranging from 3 to 65, or, optionally, repeating units offormula (VI) ##STR42## wherein Y is aryl or alkyl and p is an integerranging from 5 to 30, with a trimellitic anhydride in dioxane followedby removal of dioxane under pressure vacuum and thermal treatment. 12.The process according to claim 10, wherein the polymerizing monomer isobtained by condensing two moles of a para- or meta-hydroxycarboxylicacid of formula (XVI) ##STR43## with one mole of an acetoxy compound offormula (XII) ##STR44## followed by acylation of hydroxy groups, or bycondensing in pyridine two moles of an acetoxy carboxylic acid chloridederived from a compound of formula (XI) ##STR45## with one mole of adihydroxy compound of formula (XVII) ##STR46## wherein z is hydrogen,alkyl, alkoxy, aryl or halogen, and w is zero or one, followed byprecipitation and extraction in methanol and drying.
 13. A compoundwhich comprises a polymer matrix consisting of a thermoplastic polymerand a liquid crystalline polymer blended with the matrix, characterizedin that the liquid crystalline polymer comprises a blockcopolyesterimide according to claim
 1. 14. A compound according to claim13, wherein the polymer matrix consists of a polyolefin or apolyolefinic copolymer, of a polyester, a polyamide or a polyether.